Production of benzoic acid



' J. B. SENDEREN' PRODUCTlON 0F BENZOI D.

APPLICATION FILED-1U Lvl. 1919'.

v 13,365,956.4 Patented-Jan. 18,1921.

Fs s 2 I @EBI-jf UNITED STATES,

PATENT OFFICE.

JEAN BAPTISTE SENDEBENS, OF CHISY-LE-ROI, FRANCE, ASSIGNOR T0 LES ETAB- LISSEMENTS POULENC FIRJJRES,l 0F PARIS, FRANCE.

PRODUCTION 0F BENZOIC ACID.

Specication of Letters Patent.

Patented Jan. 18, 1921.

Application led July 7, 1919. Serial No. 309,195.

dioxid of manganese and sulfuric acid relav tively to organic substances has long been known.

The reaction has been applled to the preparation of various compounds and more particularly to the manufacture of benzaldehyde from toluene as a basls. (See French Patent 276258 of March 29th 1898 and patent of addition of May 3rd 1899).

The product was obtained by the following reactions The" oxygen being furnished by the reaction.

But an oxidation which leads to benzoic acid may also be used.

a cHscHa-toazdmcoznango This oxidation may be carried further and according to Carius may lead to phtalic acid.

It has however now been found that a much more advanced oxidation is possible yielding almost exclusively water and carbonio acid gas'.

5. cemcnomzinzowco.

o,H eco 311,0 00H4 4 2H these conditions is only formed in very small quantities, but if attempts are made to considerably raise these temperatures the conditions of equation (5) apply and instead of benzoic acid we obtain carbonio acid gas, and water.

Such are the difficulties encountered in the preparation of benzoic acid by oxidation of toluene by means of manganese dioxid and sulfuric acid and which explainthe absence of any patent relating to this process. It is perhaps in order to overcome these diiiculties that, in the preparation of nitro-benzoic acids, certain authors advise oxidizing nitrotoluenes with manganese dioxid and sulfuric acid of 40 B, at the temperature of 135 l C. 145 C but under pressure.

According to the present invention benzoic acid is produced by a different and much more simple method.

The production of benzoic acid by oxidation of toluene is the resultant of two reactlons;

(a) 3MnO2+3SO4HzzSO4Mn+3H2O+03 (b) 06H5.CH3+O3;.:C8H5.CO2H+H2O These reactions are exothermic.

The applicant has in fact ascertained that they take -place with the release of heat at ordinary tem erature very vigorously with sulfuric aci of 66 and moderately with acid of 52 B.v

With this latter acid it is well to start the reaction by brin ing the mixture to the proximity of 50. hen the temperature rises and a release of CO2 will 'soon be observed which indicates a partial destruction of toluene orl the benzoic acid formed.

This release of gas will increase' with the rise of temperature if the recaution is not taken to cool the mass. he cooling must not however be too great because if the temperature falls to 40 and below, only alde hyde is obtained, while on the contrary ben- Azoic acid is produced almost exclusively at the high temperature nearestto itsdestruction. This temperature varies with the various manganese dioxids used according as they are more or less leasily acted on by sulfurie acid; -but it is determined in all cases by a commencement of the release of as which must always be kept very small. or this object the autoclave in which the reaction 1s conducted is connected with a gas meter which is preferably calibrated in liters the indicating pointer'having avery small vrange of movement..

The temperature which suits theV reaction having been obtained it must be maintained by suitable cooling because it always tends to increase spontaneously.` It is preferable not to introduce thewhole of the man anese dioxid and the sulfuric acid of 53 into the ltoluene at once but rather gradually The operation is .terminated when, in the absence of any` articial cool1ng, the temperature spontaneously commences tofall which is; indicated by a thermometer and by a retrograde movement. of the 4pointer of the meter.v v v The invention will-be further described by aid of anexample illustrated; bythe accompanying drawing; 200. kilograms of toluene 'are introduced into a vat A as shown in Fig. 1, having a double bottom 'and leadlined or-enameled internally and having a capacity of .2500 liters, hermetically closed With a cover through which a thermometer T passes. The vat is provided with anagitator K and communicates with a gas meter C. vWhen the agitator has been started 400 kilograms of manganese dioxid are 2added in 8 or 10 operations and 2000 kilograms of sulfuric acid of 532-530 B., these additions being distributed so as to have but a very slight levolution of CO2.. At the conimencement the temperature is raised to about L10-50 if necessary in order to start the reaction, by means'of a steam pipe connecting with the double bottom. A cold water pipe allows of the desired temperature which varies between 60 and 70 being maintained, according as the manganese dioxid is more or less easily acted on by the sulfuric acid.4 Generally the introduction i of the whole of the dioxid and the whole of the sulfuric acid requires 12 to 14 hours and the reaction continues for a further `6 to 8 hours. After this time the fall in the temperature indicates the end of the operation.

VThe agitator is then stopped and the semiliquid mixture is then run into a vat B where on cooling it separates into three layers as shown in Fig. 2.

(a)` A solid layer formed of beiizoic acid mixed with toluene and a little benzaldehyde;

(b) A liquid layer formed of an acid solution of sulfate of manganese; and

(c) A solid layer of oxids of manganese.

The layer a of benzoic acid when treated with a solution of carbonate of soda yields benzoate of soda, at the surface of which iioats the mixture of toluene and benzalde- :hyde which may be separated therefrom by means of bisulfite of soda.

The benzoate of soda treated by hydrochloric or sulfuric acid yields benzoic acid the purification of which is effected by sublimation orV crystallization.

The 200 kilograms of toluene employed yield approximately Benzoic acid 100 kilograms' Benz aldehyde 8 -Toluene recovered- 100 I declare that what I claim is 1. A process for the manufacture of benzoic acid from toluene by the oxidizing reaction with a mixture of sulfuric acid and manganese dioxid in which the reaction is mairtained at a temperature from G0O to 2. A process for the manufacture of benzoic acid from toluene b the oxidizing reaction witli a mixture .o sulfuric acid and manganese dioxid at a temperature over 500 C. but suiiiciently low that the evolution of gas can be and is maintained in extremely small quantities until the end of the reaction.

3. A process for the manufacture of benzoic acid comprising the introduction in small quantities at a time of manganese dioxid into a mixture of sulfuric acid and toluene'so that the temperature does not rise `while'ma'intaining the temperature in the .material under pressure to commence the 'reaction and then constantly cooling to maintain temperature constant in the neighborhood of 60 C. to 70o C.

6. A process for the manufacture of benzoic acid comprising oxidizing toluene by A sulfuric acid and manganese dioxid and controlling the rate of addition of the reacting substances according to the rate of generation ofthe carbon dioxid evolved.

In Witness whereof, I have hereunto signed-my name this 19th day of Juno 1010. in the presence of two subscribing witnesses.

JEAN BAPTISTE SENDERENS.

Witnesses ANT'oiviN MONTEILHET, JOHN F. Simons. 

